Theearthistheonlyplanetthatscientiststhinkhaslife.Whydoestheearthhavelifewhiletheotherplanets(行星)don't?Foronethingtheearthisjusttherighttemperature.Asthe_third_planetfromthesuntheearthseemsto

　　Theearthistheonlyplanetthatscientiststhinkhaslife.Whydoestheearthhavelifewhiletheotherplanets(行星)don't?Foronethingtheearthisjusttherighttemperature.Asthe_third_planetfromthesuntheearthseemstobejusttherightdistanceaway.Theplanetswhichareclosertothesunarehotthattheirsurfacesbake(烘烤)inthesun.Thefarthestplanetsarecoldballs.

　　Whentheearthdeveloped—whichscientistsbelievemayhavehappenedabout4billionyearsago—manygasescoveredtheearth.Thegasescausedtheearthtobehot.Butsomethingwonderfulhappened.Thetemperaturewasjustrightforthickcloudstoform.Itrainedveryhardforaverylongtime.Thisgavetheearthitsoceans.Watermadeitpossibleforplantstogrow.Theplantscreatedoxygenintheatmosphere.Oxygenisthegasthathumansandanimalsbreathe.

　　Onlyoneotherplanetinthesolarsystemseemstobesomethingliketheearth.ThatplanetisMars(火星).Marsissmallerthantheearthanditisquiteabitcooler.Butitisnottoocoldforhumans.OnsomedaysthetemperaturesareaslowasawinterdayinthenorthernUnitedStates.IfyouworeaspecialspacesuityoucouldwalkaroundonMars.YouwouldhavetobringyourownairtobreathetheaironMarsistoothintobreathe.

　　Marshasthelargestvolcano(火山)inthesolarsystem.Itissixteenmileshigh.Thehighestvolcanoontheearthisfivemileshigh.Themostunexpected(未预测到的)sightonMarsisdriedupriverbeds.ScientistsbelievethatMarswasoncemuchbetterthanitisnow.DoesthismeantherecouldhavebeenlivingthingsonMars?Scientistsarenotsurebuttherehasbeennosignsofar.

　　小题1:WhichofthefollowingisNOTthereasonthattheearthhaslife?A．Theearthisjusttherighttemperature.B．ThevolcanosoneartharelowerthanthoseonMars.C．Thereisoxygenintheatmosphereoftheearth.D．Theearthseemstobejusttherightdistanceawayfromthesun.小题2:Theunderlinedphrase“thethirdplanet”inthefirstparagraphrefersto________.A．theSunB．theMoonC．theEarthD．theMars小题3:WhichofthefollowingabouttheMarsisNOTtrue?A．There